Separator for a high energy rechargeable lithium battery

ABSTRACT

The instant invention is directed to a separator for a high energy rechargeable lithium battery and the corresponding battery. The separator includes a ceramic composite layer and a polymeric microporous layer. The ceramic layers includes a mixture of inorganic particles and a matrix material. The ceramic layer is adapted, at least, to block dendrite growth and to prevent electronic shorting. The polymeric layer is adapted, at least, to block ionic flow between the anode and the cathode in the event of thermal runaway.

FIELD OF THE INVENTION

A separator for a high energy rechargeable lithium battery and a highenergy rechargeable lithium battery are disclosed herein.

BACKGROUND OF THE INVENTION

A high energy rechargeable lithium battery has an anode with an energycapacity of at least 372 milliampere-hours/gram (mAh/g). Such anodesinclude, for example, lithium metal, lithium alloys (e.g. lithiumaluminum), and mixtures of lithium metal or lithium alloys and materialssuch as carbon, nickel, and copper. Such anodes exclude anodes solelywith lithium intercalation or lithium insertion compounds.

The commercial success of lithium metal or lithium alloy batteries haseluded all but primary cells due to persistent safety problems.

The difficulties associated with the use of the foregoing anodes stemmainly from lithium dendrite growth that occurs after repetitivecharge-discharge cycling. (While dendrite growth is a potential problemwith any lithium battery, the severity of the problem with theabove-mentioned high energy anodes is much greater than with otherlithium anodes (e.g. pure carbon intercalation anodes) as is well knownin the art.) When lithium dendrites grow and penetrate the separator, aninternal short circuit of the battery occurs (any direct contact betweenanode and cathode is referred to as “electronic” shorting, and contactmade by dendrites is a type of electronic shorting). Some shorting(i.e., a soft short), caused by very small dendrites, may only reducethe cycling efficiency of the battery. Other shorting may result inthermal runaway of the lithium battery, a serious safety problem forlithium rechargeable battery.

The failure to control the dendrite growth from such anodes remains aproblem, limiting the commercialization of cells with those anodes,particularly those cells with liquid organic electrolytes.

Accordingly, there is a need to improve high energy rechargeable lithiumbatteries.

SUMMARY OF THE INVENTION

The instant invention is directed to a separator for a high energyrechargeable lithium battery and the corresponding battery. Theseparator includes at least one ceramic composite layer and at least onepolymeric microporous layer. The ceramic composite layer includes amixture of inorganic particles and a matrix material. The ceramiccomposite layer is adapted, at least, to block dendrite growth and toprevent electronic shorting. The polymeric layer is adapted, at least,to block ionic flow between the anode and the cathode in the event ofthermal runaway.

DETAILED DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a sectional view of a lithium metal battery.

FIG. 2 is a cross-sectional view of the separator.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the figures, wherein like numerals indicate like elements,there is shown in FIG. 1 a lithium metal battery (or cell) 10. Lithiummetal cell 10 comprises a lithium metal anode 12, a cathode 14, and aseparator 16 disposed between anode 12 and cathode 14, all of which ispackaged within a can 20. The illustrated cell 10 is a cylindrical cellor ‘jelly roll’ cell, but the invention is not so limited. Otherconfigurations, for example, prismatic cells, button cells, or polymercells are also included. Additionally, not shown is the electrolyte. Theelectrolyte may be a liquid (organic or inorganic), or a gel (orpolymer). The invention will be, for convenience, described with regardto a c ylindrical cell with a liquid organic electrolyte, but it is notso limited and may find use in other cell types (e.g. energy storagesystem, combined cell and capacitor) and configurations.

The anode 12 should have an energy capacity greater than or equal to 372mAh/g, preferably ≥700 mAh/g, and most preferably ≥1000 mAH/g. Anode 12may be constructed from a lithium metal foil or a lithium alloy foil(e.g. lithium aluminum alloys), or a mixture of a lithium metal and/orlithium alloy and materials such as carbon (e.g. coke, graphite),nickel, copper. The anode 12 is not made solely from intercalationcompounds containing lithium or insertion compounds containing lithium.

The cathode 14 may be any cathode compatible with the anode and mayinclude an intercalation compound, an insertion compound, or anelectrochemically active polymer. Suitable intercalation materialsincludes, for example, MoS₂, FeS₂, MnO₂, TiS₂, NbSe₃, LiCoO₂, LiNiO₂,LiMn₂O₄, V₆O₁₃, V₂O₅, and CuCl₂. Suitable polymers include, for example,polyacetylene, polypyrrole, polyaniline, and polythiopene.

The electrolyte may be liquid or gel (or polymer). Typically, theelectrolyte primarily consists of a salt and a medium (e.g. in a liquidelectrolyte, the medium may be referred to as a solvent; in a gelelectrolyte, the medium may be a polymer matrix). The salt may be alithium salt. The lithium salt may include, for example, LiPF₆, LiAsF₆,LiCF₃SO₃, LiN(CF₃SO₃)₃, LiBF₆, and LiClO₄, BETTE electrolyte(commercially available from 3M Corp. of Minneapolis, MN) andcombinations thereof. Solvents may include, for example, ethylenecarbonate (EC), propylene carbonate (PC), EC/PC,2-MeTHF(2-methyltetrahydrofuran)/EC/PC, EC/DMC (dimethyl carbonate),EC/DME (dimethyl ethane), EC/DEC (diethyl carbonate), EC/EMC(ethylmethyl carbonate), EC/EMC/DMC/DEC, EC/EMC/DMC/DEC/PE, PC/DME, andDME/PC. Polymer matrices may include, for example, PVDF (polyvinylidenefluoride), PVDF:THF (PVDF:tetrahydrofuran), PVDF:CTFE (PVDF:chlorotrifluoro ethylene) PAN (polyacrylonitrile), and PEO (polyethyleneoxide).

Referring to FIG. 2, separator 16 is shown. Separator 16 comprises aceramic composite layer 22 and a polymeric microporous layer 24. Theceramic composite layer is, at least, adapted for preventing electronicshorting (e.g. direct or physical contact of the anode and the cathode)and blocking dendrite growth. The polymeric microporous layer is, atleast, adapted for blocking (or shutting down) ionic conductivity (orflow) between the anode and the cathode during the event of thermalrunaway. The ceramic composite layer 22 of separator 16 must besufficiently conductive to allow ionic flow between the anode andcathode, so that current, in desired quantities, may be generated by thecell. The layers 22 and 24 should adhere well to one another, i.e.separation should not occur. The layers 22 and 24 may be formed bylamination, coextrusion, or coating processes. Ceramic composite layer22 may be a coating or a discrete layer, either having a thicknessranging from 0.001 micron to 50 microns, preferably in the range of 0.01micron to 25 microns. Polymeric microporous layer 24 is preferably adiscrete membrane having a thickness ranging from 5 microns to 50microns, preferably in the range of 12 microns to 25 microns. Theoverall thickness of separator 16 is in the range of 5 microns to 100microns, preferably in the range of 12 microns to 50 microns.

Ceramic composite layer 22 comprises a matrix material 26 havinginorganic particles 28 dispersed therethrough. Ceramic composite layer22 is nonporous (it being understood that some pores are likely to beformed once in contact with an electrolyte, but ion conductivity oflayer 22 is primarily dependent upon choice of the matrix material 26and particles 28). The matrix material 26 of layer 22 differs from theforegoing polymer matrix (i.e., that discussed above in regard to themedium of the electrolyte) in, at least, function. Namely, matrixmaterial 26 is that component of a separator which, in part, preventselectronic shorting by preventing dendrite growth; whereas, the polymermatrix is limited to the medium that carries the dissociated salt bywhich current is conducted within the cell. The matrix material 26 may,in addition, also perform the same function as the foregoing polymermatrix (e.g. carry the electrolyte salt). The matrix material 26comprises about 5-80% by weight of the ceramic composite layer 22, andthe inorganic particles 28 form approximately 20-95% by weight of thelayer 22. Preferably, composite layer 22 contains inorganic particles30%-75% by weight. Most preferably, composite layer 22 containsinorganic particles 40%-60% by weight.

The matrix material 26 may be ionically conductive or non-conductive, soany gel forming polymer suggested for use in lithium polymer batteriesor in solid electrolyte batteries may be used. The matrix material 26may be selected from, for example, polyethylene oxide (PEO),polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE),polyurethane, polyacrylonitrile (PAN), polymethylmethacrylate (PMMA),polytetraethylene glycol diacrylate, copolymers thereof, and mixturesthereof. The preferred matrix material is PVDF and/or PEO and theircopolymers. The PVDF copolymers include PVDF:HFP (polyvinylidenefluoride:hexafluoropropylene) and PVDF:CTFE (polyvinylidenefluoride:chlorotrifluoroethylene). Most preferred matrix materialsinclude PVDF:CTFE with less than 23% by weight CTFE, PVDH:HFP with lessthan 28% by weight HFP, any type of PEO, and mixtures thereof.

The inorganic particles 28 are normally considered nonconductive,however, these particles, when in contact with the electrolyte, appear,the inventor, however, does not wish to be bound hereto, to develop asuperconductive surface which improves the conductivity (reducesresistance) of the separator 16. The inorganic particles 28 may beselected from, for example, silicon dioxide (SiO₂), aluminum oxide(Al₂O₃), calcium carbonate (CaCO₃), titanium dioxide (TiO₂), SiS₂, SiPO₄and the like, or mixtures thereof. The preferred inorganic particle isSiO₂, Al₂O₃, and CaCO₃. The particles may have an average particle sizein the range of 0.001 micron to 25 microns, most preferably in the rangeof 0.01 micron to 2 microns.

The microporous polymeric layer 24 consists of any commerciallyavailable microporous membranes (e.g. single ply or multi-ply), forexample, those products produced by Celgard Inc. of Charlotte, NorthCarolina, Asahi Chemical of Tokyo, Japan, and Tonen of Tokyo, Japan. Thelayer 24 has a porosity in the range of 20-80%, preferably in the rangeof 28-60%. The layer 24 has an average pore size in the range of 0.02 to2 microns, preferably in the range of 0.08 to 0.5 micron. The layer 24has a Gurley Number in the range of 15 to 150 sec, preferably 30 to 80sec. (Gurley Number refers to the time it takes for 10 cc of air at 12.2inches of water to pass through one square inch of membrane.) The layer24 is preferably polyolefinic. Preferred polyolefins includepolyethylene and polypropylene. Polyethylene is most preferred.

The foregoing separator, while primarily designed for use in high energyrechargeable lithium batteries, may be used in other battery systems inwhich dendrite growth may be a problem.

The foregoing shall be further illustrated with regard to the followingnon-limiting examples.

EXAMPLES

Sixty (60) parts of fine particle calcium carbonate, 40 parts ofPVDF:HFP (Kynar 2801), are dissolved in 100 parts of acetone at 35° C.for 3 hours under high shear mixing. The solution is cast into a 15micron film. After vaporization of the actone at room temperature, thecomposite film was thermally laminated with 2 layers (8 microns) ofCelgard 2801 membrane. The resulting composite shutdown separator has astructure of PE/composite/PE and a thickness of 30 microns.

Thirty (30) parts of silicon dioxide, 30 parts of calcium carbonate, 40parts of PVDF:HFP (Kynar 2801) are dissolved in 100 parts of acetone at35° C. for 3 hours under high shear mixing. This solution was cast orcoated onto a 23 micron layer of a polyethylene microporous layer madeby Celgard Inc. After vaporization of the acetone at room temperature,the polyethylene/composite membrane had a thickness of 38 microns.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification, as indicating the scope of theinvention.

What is claimed is:
 1. A separator for a high energy rechargeablelithium battery comprises: at least one ceramic composite layer, saidlayer including a mixture of inorganic particles in a matrix material;said layer being adapted to at least block dendrite growth and toprevent electronic shorting; and at least one polyolefinic microporouslayer, said layer being adapted to block ionic flow between an anode anda cathode.
 2. The separator according to claim 1 wherein said mixturecomprises between 20% to 95% by weight of said inorganic particles andbetween 5% to 80% by weight of said matrix material.
 3. The separatoraccording to claim 1 wherein said inorganic particles are selected fromthe group consisting of SiO₂, Al₂O₃, CaCO₃, TiO₂, SiS₂, SiPO₄, andmixtures thereof.
 4. The separator according to claim 1 wherein saidmatrix material is selected from the group consisting of polyethyleneoxide, polyvinylidene fluoride, polytetrafluoroethylene, polyurethane,polyacrylonitrile, polymethylmethacrulate, polytetraethylene glycoldiacrylate, copolymers thereof, and mixtures thereof.
 5. The separatoraccording to claim 1 wherein said polyolefinic microporous layer is apolyolefinic membrane.
 6. The separator according to claim 5 whereinsaid polyolefinic membrane is a polyethylene membrane.
 7. A separatorfor a high energy rechargeable lithium battery comprises: at least oneceramic composite layer or coating, said layer including a mixture of20-95% by weight of inorganic particles selected from the groupconsisting of SiO₂, Al₂O₃, CaCO₃, TiO₂, SiS₂, SiPO₄, and mixturesthereof, and 5-80% by weight of a matrix material selected from thegroup consisting of polyethylene oxide, polyvinylidene fluoride,polytetrafluoroethylene, copolymers of the foregoing, and mixturesthereof; and at least one polyolefinic microporous layer having aporosity in the range of 20-80%, an average pore size in the range of0.02 to 2 microns, and a Gurley Number in the range of 15 to 150 sec. 8.The separator according to claim 7 wherein said inorganic particles havean average particle size in the range of 0.001 to 24 microns.
 9. Theseparator according to claim 7 wherein said inorganix particles areselected from the group consisting of SiO₂, Al₂O₃, CaCO₃, and mixturesthereof.
 10. The separator according to claim 7 wherein said matrixmaterial is selected from the group consisting of polyvinylidenefluoride and/or polyethylene oxide, their copolymers, and mixturesthereof.
 11. A high energy rechargeable lithium battery comprising: ananode containing lithium metal or lithium-alloy or a mixtures of lithiummetal and/or lithium alloy and another material; a cathode; a separatoraccording to claims 1-10 disposed between said anode and said cathode;and an electrolyte in ionic communication with said anode and saidcathode via said separator.
 12. A separator for an energy storage systemcomprises: at least one ceramic composite layer or coating, said layerincluding a mixture of 20-95% by weight of inorganic particles selectedfrom the group consisting of SiO₂, Al₂O₃, CaCO₃, TiO₂, SiS₂, SiPO₄, [andthe like] and mixtures thereof, and 5-80% by weight of a matrix materialselected from the group consisting of polyethylene oxide, polyvinylidenefluoride, polytetrafluoroethylene, copolymers of the foregoing, andmixtures thereof, said layer being adapted to at least block dendritegrowth and to prevent electronic shorting; and at least one polyolefinicmicroporous layer having a porosity in the range of 20-80%, an averagepore size in the range of 0.02 to 2 microns, and a Gurley Number in therange of 15 to 150 sec, said layer being adapted to block ionic flowbetween an anode and a cathode.
 13. A separator for a rechargeablelithium battery comprising: at least one ceramic composite layer whereinthe ceramic composite layer includes a mixture of inorganic particles ina matrix material and wherein the ceramic composite layer is adapted toat least block dendrite growth after repetitive charge-discharge cyclingand to prevent electronic shorting, wherein the ceramic composite layeris nonporous such that pores are formed once in contact with anelectrolyte; and at least one polyolefinic microporous layer wherein thelayer is adapted to block ionic flow between an anode and a cathode. 14.The separator according to claim 13 wherein the ceramic composite layeris a coating.
 15. The separator according to claim 14 wherein thecoating thickness is in the range of about 0.01 to 25 microns.
 16. Theseparator according to claim 13 wherein the matrix material comprisespolyethylene oxide (PEO), polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), polyurethane, polyacrylonitrile (PAN),polymethylmethacrylate (PMMA), polytetraethylene glycol diacrylate,copolymers thereof, or mixtures thereof.
 17. The separator according toclaim 16 wherein the matrix material comprises polyvinylidene fluoride(PVDF), polyethylene oxide (PEO), copolymers thereof, or mixturesthereof.
 18. The separator according to claim 13 wherein the matrixmaterial comprises a gel forming polymer.
 19. The separator according toclaim 13 wherein the matrix material is a continuous material in whichthe inorganic particles are embedded.
 20. The separator according toclaim 13 wherein the inorganic particles have an average particle sizein the range of 0.001 to 24 microns.
 21. The separator according toclaim 13 wherein the inorganic particles comprise silicon dioxide(SiO₂), aluminum oxide (Al₂O₃), calcium carbonate (CaCO₃), titaniumdioxide (TiO₂), SiS₂, SiPO₄, or mixtures thereof.
 22. The separatoraccording to claim 13 wherein the inorganic particles comprise silicondioxide (SiO₂), aluminum oxide (Al₂O₃), calcium carbonate (CaCO₃), ormixtures thereof.
 23. The separator according to claim 13 wherein thepolyolefinic microporous layer comprises polyethylene or polypropylene.24. The separator according to claim 13 wherein the polyolefinicmicroporous layer is a polyolefinic membrane.
 25. The separatoraccording to claim 24 wherein the polyolefinic membrane is apolyethylene membrane.
 26. The separator according to claim 13 whereinthe ceramic composite layer prevents electronic shorting by eliminatingsoft shorts caused by dendrites.
 27. The separator according to claim 13wherein the ceramic composite layer prevents electronic shorting byeliminating soft shorts caused by dendrites that grow during repetitivecharge-discharge cycling.
 28. A separator for a rechargeable lithiumbattery comprising: at least one ceramic composite layer, wherein theceramic composite layer comprises: a mixture of about 20-95% by weightof inorganic particles, and about 5-80% by weight of a matrix material,wherein the ceramic composite layer is adapted to at least blockdendrite growth after repetitive charge-discharge cycling and thereby toprevent electronic shorting and the ceramic composite layer is nonporoussuch that pores are formed once in contact with an electrolyte; and atleast one polyolefinic microporous layer having a porosity in the rangeof about 20-80%, an average pore size in the range of about 0.02 to 2microns, and wherein the polyolefinic microporous layer is adapted toblock ionic flow between an anode and a cathode.
 29. The separatoraccording to claim 28 wherein the ceramic composite layer is a coating.30. The separator according to claim 29 wherein the coating thickness isin the range of about 0.01 to 25 microns.
 31. The separator according toclaim 28 wherein the matrix material comprises polyethylene oxide (PEO),polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE),polyurethane, polyacrylonitrile (PAN), polymethylmethacrylate (PMMA),polytetraethylene glycol diacrylate, copolymers thereof, or mixturesthereof.
 32. The separator according to claim 31 wherein the matrixmaterial comprises polyvinylidene fluoride (PVDF), polyethylene oxide(PEO), copolymers thereof, or mixtures thereof.
 33. The separatoraccording to claim 28 wherein the matrix material comprises a gelforming polymer.
 34. The separator according to claim 28 wherein thematrix material is a continuous material in which the inorganicparticles are embedded.
 35. The separator according to claim 28 whereinthe inorganic particles have an average particle size in the range ofabout 0.001 to 24 microns.
 36. The separator according to claim 28wherein the inorganic particles comprise silicon dioxide (SiO₂),aluminum oxide (Al₂O₃), calcium carbonate (CaCO₃), titanium dioxide(TiO₂), SiS₂, SiPO₄, or mixtures thereof.
 37. The separator according toclaim 36 wherein the inorganic particles comprise silicon dioxide(SiO₂), aluminum oxide (Al₂O₃), calcium carbonate (CaCO₃), or mixturesthereof.
 38. The separator according to claim 28 wherein the ceramiccomposite layer prevents electronic shorting by eliminating soft shortscaused by dendrites.
 39. The separator according to claim 28 wherein theceramic composite layer prevents electronic shorting by eliminating softshorts caused by dendrites that grow during repetitive charge-dischargecycling.